Fury star Shia LaBeouf has said he pushes himself to extremes because he lacks confidence in his acting.

The 28-year-old actor had a tooth removed and cut his face with a knife to create convincing war wounds for his role as Boyd "Bible" Swan in David Ayer's Second World War film, which closed the BFI London Film Festival tonight.

"I'm not a really confident actor. I don't have faith in my abilities or my skill set," he said at the film's European premiere in London's Leicester Square.

The Transformers star, who started performing as a child, continued: "It's like if I told you to react to a gunshot right now. It would be much easier if I just got a gun out and pulled the trigger because you wouldn't have to conjure anything. You would just react to it. I try to alter my life so that I don't have to conjure anything or to make believe."

LaBeouf, whose Fury co-stars include Brad Pitt, Logan Lerman, Michael Pena and Jon Bernthal, played down the boot camp, calling it a "camping trip" but said of the gruelling training: "It was more than a physical thing, it was psychological.

"They built situations that were doomed to fail so you couldn't win. You get to 100 push-ups and they'd say 100 more, then when you do that it would be 100 more.

"You have to rely on each other because if I can't do it, Jon's got to do it. And if he can't Mike's got to do them and so forth. You learn to relinquish yourself as the 'we' of it rather than the 'I'. It takes the selfishness away."

He said the film is different from other war movies.

"This movie is about war but it's really about intimacy amongst men," he explained.

"War is the only place where men can unconditionally love one another in society and I hope that's what we captured."

Fury opens in cinemas on October 22.